Boilers, driers, furnaces, gasifiers, incinerators, ovens, and other combustion units used in industrial processes require monitoring of one or more burner or pilot flames for safety and quality control purposes. Each combustion unit typically employs a control system with one or more flame detection devices coupled to a flame sensing circuitry. These flame detection devices allow furnace operators to shut down fuel and air supply in the event of a flame failure and to adjust burner controls to change flame characteristics such as flame length and firing rate.
Common flame detection devices include flame rods—which use flame conductivity as a detection means—photosensitive conductors, which use compounds that are electrically sensitive to the flame, and photoelectric detectors that respond to infrared and ultraviolet radiation. These detection devices, however, have significant disadvantages. See Ganeshan, U.S. Pat. No. 6,278,374. Flame rods experience thermal degradation and a relatively short life span because the tip of the rod must remain in constant contact with the burner flame or pilot flame. Photosensitive and photoelectric devices are limited in their construction to materials which can withstand high temperature, and the devices are adversely affected by dust and must be periodically purged with air. More importantly, none of the devices are capable of monitoring multiple burners and all of the devices are extremely limited in their analysis of the combustion process.
To allow for the monitoring of multiple burners with a single flame detection device, and to provide for improved qualitative and quantitative analysis of the combustion process, analog and digital cameras are increasingly being used. One or more cameras are positioned to acquire an image of one or more burner or pilot flames. The camera may be fitted with a charge-control device, have a UV or infrared lens or filter, and may include an optical probe. Characteristic parameters of the flame are then derived directly from the flame image using various algorithms and compared to one or more reference flame measurements.
Although cameras provide for improved qualitative and quantitative analysis of the flame, the cameras are not immune to the extreme heat and dust that adversely affects the performance of conventional detection devices. Therefore, a need exists for a sensor housing system that adequately protects a camera and other detection devices from extreme heat and dust.